The Image by Wim van Egmond (NL)
Text By Brian Darnton (GB)
It is a pursuit that still occupies many of our modern day rulers; mining and laborious extraction from sea water remain the only methods that really work!
Silver is another matter. During the last century a crew of seamen were set to work recovering a useful sunken copper clad vessel that had gone down in South America. I am not going to tell you which river that was, I already have my bags packed! When they hauled the hull from the river sand at low tide they were presented with an incredulous situation. Rather than copper, it was clad in silver plate. The ship's scientist realised at once that the river water contained silver salts and that the copper had caused the silver to be precipitated as pure silver as exchange took place.
The Victorians used to enjoy creating silver under the microscope from silver nitrate in solution. The arborescent patterns were intriguing and highly decorative. These are the sort of configurations one can also create from a certain type of fractal on ones PC.
Solid silver nitrate is still available as a wart stick. If the terminal 2mm is cut off with a sharp scalpel it can be dropped into a 30ml. brown or dark bottle of clean water. Use a pair of forceps to handle the stick because it will turn human tissue and clothing brown and very unsightly. The solution is similarly caustic and poisonous and must be stored securely and correctly labelled. It is best conserved when kept in the dark as sunlight degrades the solution.
Place a single drop of the solution in the centre of a glass cell and place a copper strand of wire so that it touches the solution. With a little warmth from a lamp, a tree like crystal of pure silver will have formed. The Victorians had a method of washing out the copper nitrate that was produced but if the whole is simply dried out then the crystals of copper nitrate will act as an adhesive. Provided the cell is dry sealed it will remain in "mint" condition for a long time. The use of several copper strands around the perimeter of the drop will create converging patterns. More dilute solutions will produce finer crystals.
Remember to beware of the caustic silver solution!
IMPORTANT SAFETY NOTICE
Editor's Note: to emphasise the author's note of caution.
Silver nitrate solid is classed as CORROSIVE.
Silver nitrate solution is classed as both CORROSIVE and OXIDISING.
Children should not carry out this experiment without proper adult supervision. In general, skin contact, ingestion and eye contact should be avoided. As with handling all hazardous chemicals, suitable protective gloves, eye protection and proper working area for handling and disposing of chemicals at least should be adopted. No responsibility is accepted by the owners, administrators or contributors to On.View Ltd., Microscopy-UK or Micscape for damage to property or persons by carrying out this experiment.
Published in December 1998 Micscape Magazine.
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